Variable speed friction drive

ABSTRACT

A variable speed planetary transmission in which a plurality of drive components are constructed in the form of interfaced conical friction members mounted for rotation about parallel axes and axially and radially relatively manipulatable to provide variable ratio gearing members. A preferred embodiment embodies planet rollers of a double conical configuration in rolling contact with mating rollers of reverse conical configuration and in which axial control means are provided for manipulating the axial positions of the cooperating conical members to provide a variable speed connection between sun and ring gear members. A further embodiment of the invention provides a differential variable speed drive wherein multiconical epicyclic transmission elements are employed to provide a varying output smoothly infinitely adjustable from a high forward speed downwardly through zero output to reverse speed, all without requiring a variation in the speed of rotation to the input shaft of the transmission.

United States Patent r191 Nasvytis 1 Feb. 26, 1974 1 VARIABLE SPEEDFRICTION DRIVE [76] Inventor: Algirdas L. Nasvytis, 10823 Magnolia,Cleveland, Ohio 44106 [22] Filed: Oct. 2, 1972 [21] Appl. No.: 294,016

[56] References Cited UNITED STATES PATENTS 2,205,768 Pearce, Jr.

2,209,497 7/1940 Winger et a1. 2,696,888 12/1954 Chillson et a1 74/796 X2,973,671 Elkins 74/796 Primary Examiner-Arthur McKeon Attorney, Agent,or Firml-lill, Sherman, Meroni, Gross & Simpson [57] ABSTRACT I Avariable speed planetary transmission in which a plurality of drivecomponents are constructed in the form of interfaced conical frictionmembers mounted for rotation about parallel axes and axially andradially relatively manipulatable to provide variable ratio gearingmembers. A preferred embodiment embodies planet rollers of a doubleconical configuration in rolling contact with mating rollers of reverseconical configuration and in which axial control means are provided formanipulating the axial positions of the cooperating conical members toprovide a variable speed connection between sun and ring gear members. Afurther embodiment of the invention provides a differential variablespeed drive wherein multiconical epicyclic transmission elements areemployed to provide a varying output smoothly infinitely adjustable froma high forward speed downwardly through zero output to reverse speed,all without requiring a variation in the speed of rotation to the inputshaft of the transmisslon.

9 Claims, 6 Drawing Figures PATENTEB FEB 2 61974 SHEET 3 [IF 4' 3 NS mum? 6? QQQ Na w VARIABLE SPEED FRICTION DRIVE BACKGROUND OF THEINVENTION Planetary or eipcyclic transmission devices employing frictionrollers for the transmission of power, are well known in the art ofgearing. A number of proposals have been advanced for providing variablespeed friction drive systems. Perhaps the most commonly considered ofsuch devices are the toroidal mechanisms having interfacing coaxiallymounted toroidal races with one or more tiltable rollers positionedtherein for rotation about axes transverse to and intersecting the axisof rotation of the toroidal members. Other devices have embodied the useof pairs of complementary conical members combined with intermediateroller or belt force transmitting means. To my knowledge, however, suchprior systems have been unsuccessful in providing a truly satisfactory,simple, transmission capable of forward and reverse drive outputs in asimple manner. Further, experimentation with such prior systems hasindicated that friction losses, pre-loading problems, excessive wear,and the like, have prevented general adoption of any such systems inwidespread commercial use, especially for a higher horsepower range. Inaccordance with the present invention, the advantages of wide rangespeed change have been accomplished through an extremely simple systemwhich is capable, in several of its embodiments, of handling heavytorques while remaining simple in design.

SUMMARY OF THE INVENTION In a simple form of the invention, a variablespeed planetary type drive system comprises a sun roller comprising apair of axially separably disks with oppositely directed conicalsurfaces. A plurality, typically three, planets are provided forrotation with the disks and comprise axially spaced coaxial conicalmembers rotatable about an axis parallel to the axis of the sun andhaving oppositely directed conical surfaces compatible with the diskscomprising the sun but having a substantially longer axial surface thanthe sun disks. The annular ring gear constructed for cooperation withthe planet rollers comprises a pair of split disks axially separable andlikewise having conical configuration for cooperation with the planetrollers. Assuming, as one case, that the planet rollers each have amaximum radius at the centers of their axial lengths and taper towardopposite ends, then as the sun disks are adjusted axially toward eachother, the planet rollers will be forced radially outwardly and the ringdisks will be moved axially apart from each other to accommodate theradial movement. The result of such an adjustment is to provide agradually increasing gear reduction which has a maximum, when thelargest radial contact occurs between the sun roller and the planetrollers, and hence the smallest radial contact occurs between the ringgear and planet rollers. As in the case of conventional planetarysystems, the input of the drive may be attached to the sun, the planetcarrier, or the ring and, similarly, the output may comprise one or theother of the two remaining undriven elements.

It will be apparent to those familiar with the art that when disks offinite width are employed in friction engagement with conical surfaces,some slippage will occur between the edges of the disk and conicalsurface cooperating with the disk. I have found, however, that bykeeping the contact surfaces narrow and the slope of the conicalsurfaces low, the slippage is within practical limits, and actuallyenhances axial adjustment movements of the roller components.

An additional embodiment of the invention comprises the utilization ofplanet elements each consisting of a pair of dual cone roller members invariable contact with each other and rotating between compatible dualconical ring and sun element. By varying the ratio between the rollersof each planet element, and by providing a differential input to the sunand ring elements, an output is provided which ranges from a relativelyhigh forward speed downwardly through zero to a relatively lower reversespeed in a manner suitable for such transmission uses as land vehiclesor boats.

It is, accordingly, an object of the present invention to provide anovel, adjustable, friction drive system capable of smooth ratio changeover a relatively wide range and in a simple structural manner.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of afriction drive constructed in accordance with the present invention;

FIG. 2 is a cross-sectional view taken along the line 11-11 of FIG. 1;

FIG. 3 is a cross-sectional view of a second embodiment of the presentinvention;

FIG. 4 is a cross-sectional view taken along the line IV--IV of FIG. 3;

FIG. 5 is a third embodiment of the variable speed drive constructed inaccordance with the present invention and providing a planet carrierinput; and

FIG. 6 is a cross-sectional view taken along the line VI-VI of FIG. 5.

DETAILED DESCRIPTION A first embodiment of the present invention isshown in FIG. 1. There, input shaft 10 rotatably drives a sun shaft 11carrying supports 12, 13 splined thereto for rotation therewith. Theelements 12 and 13 each support conical disks 14 and 15 respectivelyhaving respective conical surfaces 16, 17. The supports 12 and 13 arethreaded, as at 18, 19 to accommodate an adjustment shaft 20 arrangedfor rotation such that rotation in one direction provides movement ofthe conical members 14 and 15 toward each other and rotation in theopposite direction provides movement thereof away from each other. Arigid planet carrier 25 supports a plurality of axial roller shafts 25ain fixed peripheral relation to each other but permitting radialmovement relative to the sun axis. The carrier 25 is in turn positivelyconnected to an output shaft 27 for rotation thereof. Each of the shafts25a carries a roller 26 having dual coned surfaces 26a and 26b forcooperation with the tapered surfaces of the ring elements 30, 31 havingrespective conical surfaces 32,33.

In the embodiment illustrated in FIG. 1, the ring elements 30 and 31 areaxially splined to subhousing 35 and are individually threaded at 36,37,respectively, to accommodate an adjustment screw 39 which is threaded toprovide for adjustment of the ring disks 30,31 toward each other uponone direction of rotation and apart from each other upon oppositerotation. In the embodiment illustrated, it will be clear that rotationof the screws 20 to move the sun disks l4 and 15 toward each otherrequires, at the same time, a simultaneous movement of the adjustmentscrew 39 to separate the ring disks 30, 31.

As shown, the input shaft of the transmission of FIG. 1 provides a splitpower path diverting some of the input to the ring 35 and some of theinput to the sun 1 1. This is accomplished by way of a first input gear40 which drives the ring 35 by way of gear 41, and a sec nd gear 42which drives the gear 43 on the end of shaft 11. As shown, the gearingprovides one direction of rotation for the ring and an oppositedirection of rotation for the sun. The gear 40 simultaneously drives thecontrol gear 44 provided with an output bevel gear 45. The gear 45drives a pair of differential gears 46 mounted upon spur shafts 47rigidly carried by a control shaft 48. Rotation of the control gear 44causes simultanerous reverse rotation control gears 50 and 51 in drivecontact with control rings 52 and 53, respectively. The gear ratiosbetween 50 and 51 and their cooperating respective control rings 52 and53 provide, when the control rod is stationary, and the gear 44 is beingrotated by the input shaft 10, a rotation of the control rings 52 and 53identical with the speed of rotation of the ring gear subcasing 35 andthe sun 11, respectively. Accordingly, when the control rod 48 isstationary, no adjustment of the adjustment screws 20 and 39 takesplace. It will be seen, however, that if the control rod 48 is rotated,during operation of the drive system, a momentary relative movement ofthe rings 52 and 53 will occur causing simultaneous counter adjustmentsof the screws 20 and 39.

As those skilled in the art of friction gearing are aware, preloading ofthe friction surfaces is essential to the transmission of substantialtorque. In the embodiment illustrated in FIGS. 1 and 2, the drive ispreloaded through the utilization of cam balls 55 positioned betweentheelements 12 and 14 (and similarly between 13 and of the sun. Each ofthe members 12 and 14 is provided with a plurality of gradually rampeddepressions each containing a ball 55. Upon relative rotation betweenelements 12 and 14 in either direction, the balls ride up the rampedside of the depression to force the members 12 and 14 axially apart,applying a preload to the drive contact. Since the planet roller 2511may radially move with respect to the planet carrier 25 to accommodateradial movement of the rollers 26 upon adjustment, preloading via theball 55 provides a preload throughout the system in a manner thatautomatically increases with an increase in the torque transmission.

The gear ratios and speeds may be varied through the ranges, of course.However, a satisfactory transmission may be constructed in generalaccordance with the embodiment illustrated in FIGS. 1 and 2 where aninput of 8,000 rpm is provided with a resultant 6,000 rpm sun rollerrotation and a 4,500 ring roller rotation in a reverse direction. Inthat embodiment, an output rotation of 166 rpm in reverse up to 2,000rpm rotation forward is provided, with a smooth traverse of that entirespeed range through zero rpm. In this arrangement, the speed ratios ofthe 6,000 rpm sun and 4,500 rpm ring represent a ring-to-sun dimensionalratio of 1.33 and the ratio provided in the illustrated embodimentbetween the sun roller and ring roller is 1:2. The double cone ratio ofthe maximum diameter to minimum diameter is 1:16 Thus, if the sun rollerand ring roller positions on the dual cone rollers 26 provide input andoutput radii that are equal, the friction drive operates with a ratio of2. If the spider is stationary with the cone rotating, a 4,500 rpm ofthe ring will force, in the absence of slipping, the sun roller will berequired to rotate 4,500 X 2 9,000 rpm. Since, however, the sun rolleris rotating as a result of gear drive contact, at 6,000 rpm, the conesmust rotate in the space at a sufficient rpm to compensate bysubtracting 3,000 rpm from the sun. If the ring roller is stationary,rotation of the carrier N rpm will force the sun to rotate (2 l rpm. Thesun rotates counterclockwise if the ring rotates clockwise and hence tosubtract sun rpm the spider rotates clockwise with N=3,000/2 1 1,000rpm. On the other hand, the smallest ratio in the friction drive occurswhen the cone radius with the sun is a minimum (r,,,,-,,) and the radiuswith the ring is r then the ratio of the drive equals 2 X ,,,,-,,/r,,2/1.6= 1.25. If the planet filler s 26 and the carrier 25 are stationaryin the space between the sun and the ring, the ring roller will forcethe sun to rotate 4,500 X 1.25 5,625 rpm or 375 rpm less than the sunrotates, whereby the carrier must rotate counterclockwise to compensatethe speed difference an amount N= 3.75/1.25 1 or 166.6 rpm. If the coneinput and output ratio is 1.5, the total drive ratio is 2/1.5 1.33 andoutput speed is zero. The maximum output rpm occurs when the drive has amaximum ratio 2 X 1.6 3.2 where N= 4,500 X 3.2 6,000/3.2 l 2,000 rpm.With the above arrangement it is clear that a rotation of the inputshaft 10 constantlyin the same direction at a substantially uniformspeed permits, by the manipulation of the control shaft 48, an outputfrom the transmission providing forward and reverse speeds without needfor shiftable clutches or brakes typically employed in transmissiondevices. Accordingly, an extremely simple structural mechanism isprovided.

As above described, the planetary friction drive provides a differentialsystem resulting from the application of input power to two elements ofthe planetary set.

In the embodiment of the invention shown in FIGS. 3 and 4, a tworowroller set is provided. In the embodiment illustrated in these Figures,the drive input is applied at the sun shaft 110. The shaft is splined at111 to carry for axial sliding but fixed rotation, a pair of sun disks112, 113 adjustably movable by way of a plurality, preferably threeequally spaced, adjusting screws 115 carried for free rotation bysupport plates 116 and 1 17 splined to the shaft 110. Adjustment of thescrews 115 is accomplished by means of a drive takeoff from input shaft110 comprising gear 120 operating as a sun gear to drive a planetcarrier 121 against a reaction ring gear 122. The planetary gears 123carried by the carrier shafts, preferably three in number, 124, carrythe shafts around the sun. An adjustment ring gear 125 is mounted formanual adjustment by means of a worm, shown in cross-section at 126.When the ring gear 125 is stationary, adjustment gear 127 moves in thesame manner as the gear 123 with the result that gear 128 riding theshaft 1 10 rotates substantially in the same manner as gear 120, withthe result that the adjustment drive gear 129 is non-rotative. This istrue since the axis of screw 115 is the same radius away from the axisof shaft 110 as is the axis of the shaft 124. When an adjustment isdesired, the worm 126 is rotated, causing a relative rotation of thering and an adjustment, either forward or reverse of the screws 115.

This adjustment causes separation or closure of the disks 112, 113.

The two-row planet system comprises dual cone outer row members 130having conical surfaces 131 and 132 which cooperate, respectively, withthe pair of split rings annulus elements 133 and 134. The members 130are rotatably carried in bearing supports 130a carried by links 13%pivotally carried by support pins 130v in the rigid carrier member 138,rotatably carried on the shaft 110 by way of bearings 139. Rollers 130cooperate with an inner row of rollers 140 by way of mating cylindricalfriction gear surfaces 141, 142, and the conical surfaces 143, 144 ofthe rollers 140 cooperate with themating tapered surfaces 112a and 113aof the respective sun disks.

Adjustment will required, of course, movement of the planet rollersrelative to each other and relative to the sun and the ring. Thus, ifthe sun disks 112, 113 are separated from each other axially, thesurfaces 112a, 113a will contact the rollers 140 at a point of smallerroller diameter which means, in turn, that the rollers 140 will moveradially toward the axis of the shaft 110 if they are to maintaincontact with the sun disks. This movement is accomplished bycorresponding movement of the rollers 130, permitted by the pivotal linksupports 130C, and the slack left by such movement is taken up bymovement of the ring annulus members 133, 134 toward each other. Thismovement is automatically accomplished by gears 135 carried by theadjusting screws 136 so that if torque is applied to the ring members133, 134 to cause an output drive of the ring carrying member 137,rotation willoccur tending to move the annuluses 133, 134 toward eachother to contact the surfaces 131, 132, respectively, and maintain suchcontact.

If in the movement of the sun disks in a ratio decreasing direction, thesun disks are moving axially toward each other and tend to force theroller sets to move radially outwardly. This action increases thepressure on the output cone contacts 131,132 and the preload must adjustto move the ring annuluses 133,134 apart. The variable speed drive formany applications will require preload mechanism which will act in bothdirections of power flow. For this reason, another gear is attached tothe power screws opposite the ring gear, as at 150, the output member137 and the gear 150 are respectively carried by rotatable spiders 151and 152 which are drivingly connected to counter shaft gears 153 and 154respectively. Although one set of gears 153,154 is adequate, a pluralityof counter shafts may readily be used to split the load. The gears153,154 are mounted on the counter shaft, shown at 155, are keyed on theshaft 155 with lost motion keys permitting 90 relative rotation betweeneach of the gears and the counter shaft. According y, one or the otherof the gears 153, 154 will free wheel depending upon the direction oftorque application applied on the shaft 155. A spring, either coil orleaf, is preferably inserted between the members 151 and 152 tending tobias them peripherally relative to each other in a direction tending tocause the annuluses 133,134 to move together at all times, therebypositively providing a preload condition of the friction conicalplanetary system independently of the direction of load or the presenceof any load.

The drive system using the two rows of planet rollers does not, in theform illustrated, provide a reverse speed or zero speed withoutsupplementary gearing. As

shown in FIG. 3, supplementary gearing may be provided in the form of areversing planetary and the inclusion of a two way clutch 161 whichselectively drives output gear 162 (in the position illustrated in FIG.3) or, upon lateral shifting to the right will drive gear 162a. Thelatter gear provides a forward speed to the output shaft 170 by way ofgear 163. Differential output is provided permitting reverse rotationthrough gear 165 at the right hand end of shaft 110. The gear 165 causesrotation of the planet carrier 166 with its planets 167 against reactionring 168. Accordingly, drive applied to the gear 160 on the carrier 166by way of gear 162 on the countershaft 155 will provide, depending uponthe ratio of output at the gear 162 from the friction transmission,either a forward or reverse movement of the shaft 170 by rotation of thegear 171 resulting from rotation of the gear 160 via annular rotatingring 172.

The transmission shown in FIGS. 3 and 4 will provide a drive from zeroto 2,000 rpm in the differential operation and from 2,000 to 5,000 rpmin a direct drive range. As those skilled in the art are aware, theefficiency of the differential drive system is somewhat lower.

In the systems described so far, it will be clear that the preloadcontrol can be made differently from the modification shown. Forexample, hydraulic actuators could be employed instead of the mechanicalscrew devices.

An important aspect of the two row planetary system is that each rollerhas three-point contact and, accordingly, the load transmitted by thesystem will be equally distributed throughout the roller complex. If oneroller were removed, for example, the entire system would collapse. Insingle row planetary systems, it has been generally recognized that anaccess of three rollers in the planet carrier provides an arrangement inwhich the load is not equally divided between the plurality of rollers.By providing the two row system shown in FIGS. 3 and 4, extremely heavytotal torque may be transmitted without overloading the individualrollers.

A still further embodiment of the invention is shown in FIGS. 5 and 6.There, a system is illustrated in which the two row planetary complex isprovided but in which no carrier support bearings are required for thetwo rows. Instead, the inner rows of rollers are each provided withpulleys and the planets are the input to the drive by way of a V-belt.Thus, as shown, the split ring gears 220 and 221 are adjustably fixed tothe housing 222 and the output of the drive is taken from the sun shaft210 carrying split sun members 211, 212. As illustrated, the sun members211, 212, respectively contact the inner row of rollers 215 via therespective conical surfaces 217, 218. The force transferred from rollers215 to the second row rollers 225 is accomplished by way of cylindricalfriction surfaces 226, 227 and the conical surfaces 229, 230 contact therespective ring annulus members 220, 221. The pulleys 231 on oppositeends of the rollers 215 are driven by V-belts 232 and conventionaltensioning devices applied to the V- belt 232 provide constant preloadof the rollers against the output shaft 210. Preload is automaticallyassured by the high pitch threads 210a, 2101) on the sun shaft 210 whichautomatically cause the sun members 211, 212 to move toward each otherunder drive conditions. Adjustment of the ring members 220, 221 isaccomplished by rotation of the adjustment screws 235 in any desiredmanner. In the embodiment illustrated in FIGS. and 6, rubber surfacesare illustrated between the friction members in each case. Thisembodiment may be employed in any of the systems illustrated, but istypically applicable in relatively low load systems. In this embodiment,forward, zero, and reverse speeds are obtainable without a specialplanetary-differential arrangement. If the instantaneous radius of thecontact 217 is called X constant radius of 226 called Y constant radius227 called X instantaneous radius of contact 229 called Y the radius ofthe ring roller 220 called C, the relation g I I (X /i4) (X lY (ClY 1,then theoutput of 210 is zero. Changing the ratio X /Y by changing theinstantaneous radius on cones 217 and 229, the total product (X /A) (X/Y (C/Y can be made less or more than one. If it is less than one, theoutput is'rotating in the same direction as the input, and if this ratiois more than one, the output of 210 is in reverse.

It will be seen from the above description and a consideration of thedrawings, that l have provided a novel system of variable speed,variable ratio, transmission device. I'have found that the efficiency ofthis improved system is very highand that it may be applied to a widerange of uses including the high horsepower automotive,uses. Theadvantages include relative sim- 7 and wherein output drive shaft indrive contact with each other and wherein successive rollers of eachplanet roller unit have oppositely tapered conical surfaces and aredrivingly connected to .each other by cylindrical roller surfaces.

. each other and wherein successive rollers of each ous to those skilledin th'e'art from a consideration of my disclosure and it is,accordingly, my intent that the ity of rotatable planet roller unitsperipherally fixedly positioned relative to a carrier, an annular ringmemher, said ring and sun being axially separably split, meanssimultaneously selectively operable to move the halves of one of saidmembers apart and to move the halves of the other member in an axialdirection to maintain contact thereof with said planet roller units,

said planet roller units comprising frusto conical units in rotativefriction contact with both the ring and sun members throughout saidselective movement.

2. Drive structure according to claim 1 wherein said planet roller-unitseach comprise a plurality of rollers planet roller unit have oppositelytapered conical surfaces for respective cooperation with said ring andsun members and are drivingly connected to each other by cylindricalroller surfaces.

6. Drive structure according to claim 1 wherein saidv sun and ringmembers are each provided with increasing taper in the direction oftaper opposite to that of the respective adjacentcontacted member. 7

7. Drive structure in accordance with claim 1 wherein gear means connectsaid drive shaft to said ring member and said sun member for rotation ofboth thereof and wherein output drive shaft means are connected to saidcarrier.

8. In combination in a drive mechanism, a sun shaft member, an annularring member, a carrier, aplurality of planet rollers carried by saidcarrier on peripherally fixed axes parallel to the axes of said sun andring members but radially movable, said sun and ring members beingaxially separably split with each half thereof being frusto conical,said planet rollers each being dual frusto conical and having each ofthe frusto conical surfaces thereof in contact with one half of therespective ring and sun members for friction drive power transmissiontherebetween, and means operable to simultaneously move the balance ofone of the members apart and the halves of the other member toward eachother to vary the drive ratio between the members.

9. The drive mechanism of claim 8 including means automaticallypreloading said members in driving engagement an increasing amount withincreasing torque transmission.

1. In combination in a drive mechanism, a rotatable drive shaft, a sunmember driven by said shaft, a plurality of rotatable planet rollerunits peripherally fixedly positioned relative to a carrier, an annularring member, said ring and sun being axially separably split, meanssimultaneously selectively operable to move the halves of one of saidmembers apart and to move the halves of the other member in an axialdirection to maintain contact thereof with said planet roller units,said planet roller units comprising frusto conical units in rotativefriction contact with both the ring and sun members throughout saidselective movement.
 2. Drive structure according to claim 1 wherein saidplanet roller units each comprise a plurality of rollers in drivecontact with each other and wherein successive rollers of each planetroller unit have oppositely tapered conical surfaces and are drivinglyconnected to each other by cylindrical roller surfaces.
 3. Drivestructure according to claim 1 wherein said sun and ring rollers areeach provided with increasing taper in the opposite direction of taperto the adjacent, contacted, member.
 4. Drive structure in accordancewith claim 1 wherein gear means connect said drive shaft to said ringmember and said sun member at differing ratios and wherein output driveshaft means are connected to said carrier.
 5. Drive structure accordingto claim 1 wherein said planet roller units each comprise a plurality ofrollers rotatable on parallel axes and in drive contact with each otherand wherein successive rollers of each planet roller unit haveoppositely tapered conical surfaces for respective cooperation with saidring and sun members and are drivingly connected to each other bycylindrical roller surfaces.
 6. Drive structure according to claim 1wherein said sun and ring members are each provided with increasingtaper in the direction of taper opposite to that of the respectiveadjacent contacted member.
 7. Drive structure in accordance with claim 1wherein gear means connect said drive shaft to said ring member and saidsun member for rotation of both thereof and wherein output drive shaftmeans are connected to said carrier.
 8. In combination in a drivemechanism, a sun shaft member, an annular ring member, a carrier, aplurality of planet rollers carried by said carrier on peripherallyfixed axes parallel to the axes of said sun and ring members butradially movable, said sun and ring members being axially separablysplit with each half thereof being frusto conical, said planet rollerseach being dual frusto conical and having each of the frusto conicalsurfaces thereof in contact with one half of the respective ring and sunmembers for friction drive power transmission therebetween, and meansoperable to simultaneously move the balance of one of the members apartand the halves of the other member toward each other to vary the driveratio between the members.
 9. The drive mechanism of claim 8 includingmeans automatically preloading said members in driving engagement anincreasing amount with increasing torque transmission.